1. Field of the Invention
The present invention relates to a motor, and more particularly, to a rotor of a motor capable of maximizing a flow path of a flux and decreasing a size thereof.
2. Description of the Conventional Art
Generally, a motor is a device for converting electric energy into kinetic energy, and the motor is being used as a driving source of many machines.
There are many types of motors, such as a direct current motor, a brushless motor, an induction motor, a synchronous motor, a universal motor, etc., depending upon its use.
FIGS. 1 and 2 are respective frontal and lateral section views showing one embodiment of a universal motor.
As shown, the universal motor comprises: a stator 100 having a through hole 111 therein; a rotor 200 rotatably inserted into the through hole 111 of the stator; a rotational shaft 300 inserted into the center of the rotor; and a commutator 400 and a brush 500 coupled to the rotational shaft 300 and supplying a current.
The stator includes: a core 110 of a certain shape; and a winding coil 120 wound on the core 110. The core 110 is provided with a through hole 111 penetrated in a longitudinal direction therein. A plurality of slots S penetrated in a longitudinal direction are formed at fixed intervals along the edge of the through hole 111, and teeth T are formed between said slots S. The slot S is composed of s an opening portion 112 connected to the through hole 111, and an extension portion 113 extendingly formed from the opening portion 112 and in which the winding coil 120 is positioned. A width of the extension portion 113 is gradually increased towards the outside of the opening portion 112, and the end of the extension portion 113 is a curved surface of a semi-circle.
The core 110 of the stator is formed as a plurality of stacked thin plates 10 having a shape corresponding to a sectional surface of the core 110.
The rotor 200 includes: a core 210 of a certain shape; and a winding coil 220 wound on the core 210. The core 210 is provided with a plurality of slots S penetrated at fixed intervals along the edge of a cylindrical body portion 211 is having a certain length in a longitudinal direction, and teeth T are formed between the slots S. As shown in FIG. 3, the slot S is composed of an opening portion 212 formed at an outer circumferential surface of the cylindrical body portion 211, and an extension portion 213 extendingly formed towards the inside of the opening portion 112 and in which the winding coil 220 is positioned. A width of the extension portion 213 is decreased towards the center of the cylindrical body portion 211, and the end of the extension portion 213 is formed as a curved surface wall 214 of a semi-circle shape. The curved surface wall 214 is located at an opposite direction from an outer circumferential surface of the cylindrical body portion 211. A width of the extension portion 213 is gradually decreased towards the inside of the opening portion 212, so that a width of a portion of each tooth located between two adjacent extension portions 213 is constant.
An axial hole 215 into which the rotational shaft 300 is inserted, is penetratingly formed at the center of the cylindrical body portion 211.
The core 210 of the rotor is formed as a plurality of stacked thin plates 20 having a shape corresponding to a sectional surface of the cylindrical body portion 211.
The operation of the universal motor will be explained as follows.
When power is supplied to the winding coil 120, a flux is formed at the stator core 110. At the same time, when power is supplied to the winding coil 220 through the brush 500 and the commutator 400, a flux is formed at the rotor core 210. By an interaction between the flux formed at the stator core 110 and the flux formed at the rotor core 210, the rotor 200 is rotated. A rotation force of the rotor 200 is transmitted to a load through the rotational shaft 300.
The universal motor is usually used as a power source of a washing machine or a vacuum cleaner, etc. A miniaturization of the universal motor is required in order to minimize a mounting space inside the washing machine or the vacuum cleaner, and the fabrication costs of the motor has to be lowered to achieve price competitiveness.
The core is one part of the universal motor that should be minimized in size and have low fabrication cost while maintaining its function.
The stator and the core constituting the rotor of the universal motor are formed as a stacked body with a plurality of thin plates having a certain shape being stacked in order to minimize power loss due to eddy current.
A shape of the core and the number of the thin plates constituting the core are set to maintain high efficiency by minimizing the loss of a flux formed at the core by the current applied to the winding coil.
However, in the conventional core of the universal motor, the inner side portion of each slot S in which the winding coil is inserted is formed as a curved surface of a semi-circle shape in order to simplify the manufacturing process when s using a punch or press. According to this, the winding coil can not be densely inserted into the slots S, which results in a decrease in an effective area of the guaranteed flux, generation of flux loss, and requiring an increased number of thin plates constituting the core.